As NASA’s next flagship space telescope is riddled with delays, the space agency is giving scientists some hard limits on how much money can be spent on future astrophysics missions. Last week, NASA announced that scientists proposing ideas for new space telescopes must limit their budgets to between $3 billion and $5 billion for the missions. The cost cap may force scientists to alter the designs of the missions they’ve been working on.

Right now, four teams of scientists are designing ambitious space telescope concepts in preparation for an upcoming report to NASA known as the 2020 Decadal Survey for Astrophysics. It’s an enormous review compiled by the National Academy of Arts and Sciences every 10 years that lists what kinds of...